1. Field of the Invention
The present invention relates to the field of methods and articles of manufacture utilizing continuous filaments.
2. Prior Art
Various techniques for the manufacture of rope are well known in the prior art. Of particular interest for the present invention is conventional or unbraided rope. Such rope may be characterized by groups of fibers or filaments twisted to provide a twine-like cord with three of the twine-like cords being twisted together in the opposite direction to form the rope. (Obviously other techniques are also well known, the foregoing being merely exemplary only.) One of the advantages of having the cords twisted in one direction and wound on themselves in the opposite direction is that the resulting rope has at least a reduced tendency to unwind when subjected to tension. Also the series of twists has the advantage of better distributing loads so that the strength of the rope will better approach the aggregate fiber strength, particularly when curved around the pulley and/or when knotted, though in both cases, particularly when tied in knots, substantial strength reduction is encountered.
For ropes of hemp and the like, techniques for splicing are well known which allow the splicing of two lengths of rope together and the splicing of eyes into the ends thereof. For ropes of synthetic fiber, however, such as nylon, etc. special splicing and knotting techniques generally must be used because of the higher strength and self-lubricating tendencies of the fiber, both of which encourage the pulling out of splices made in accordance with techniques found entirely satisfactory for hemp ropes. For the particular high strength synthetic fibers or filaments such as Kevlar which initially appear particularly attractive for use in rope of conventional construction, such rope has in fact not been used commercially because of the inability to take advantage of the rope's potential strength in any practical application.
If ordinary rope manufacturing techniques are utilized to make rope using synthetic filaments such as Kevlar, a high strength low density material having a strength-to-weight ratio on the order of five times that of steel, the resulting rope potentially has very high strength, though perhaps the abrasion resistance is inadequate for at least some uses. (Kevlar is a trademark of Dupont, used on high strength, low density synthetic filament in the nylon family.) However, in attempting to use such rope, knots reduce the potential strength considerably, with knots having a likelihood of either pulling out under the very high loads achievable or at least jamming so as to not be readily untied. If clamping is attempted rather than knotting, transverse pressure on the fibers reduces the ultimate strength of the rope. Also the rope has a tendency to pull out of such clamps because of the particularly high loads and the inability of a clamp to adequately frictionally engage the rope.
One aspect of the present invention is that the rope is formed with continuous loops at each end thereof so that the potential rope strength may be achieved in actual use by looping the ends of the rope over pins or hooks for retention. The concepts of loops at the ends of a section of cable or rope is shown in U.S. Pat. Nos. 2,199,958; 3,079,192 and 3,222,858. In the '192 patent, a cargo sling is disclosed which is formed of wire rope or the like. The sling is characterized by a rope-like assembly having a loop at each end protected by a sheath. The sling is fabricated by spacing the sheaths as desired and then hooking one end of the rope over one sheath, winding it down around the second sheath, up over the start end of the rope on the first sheath and down again, with the finished end of the rope being tucked between the loop formed by the winding and the second sheath. With this construction the load on the main loops increases the frictional engagement of the rope ends to help avoid slippage thereof. The resulting rope-like assembly is therefore comprised of three lengths of the rope or cable. In the '958 patent, a hoisting sling of generally similar construction is shown with one embodiment being formed of a single length of cable so that the body consists of three cables and the eyes consist of two cables, and the second embodiment being formed of two cables to provide a body formed of four cables and eyes consisting of three cables. The '858 patent, on the other hand, discloses a twisted cable assembly and method of making the assembly which utilizes a single strand of wire looped over a pair of spaced apart pins a substantial number of times, and then twisted about its length to form a central section of twisted wire cable with continuous loops of wire at each end thereof. In an alternate method of making the twisted cable assembly the wire is pre-twisted along its axis so that after winding around the spaced apart pins the untwisting of the individual wires will form the twist of the desired finished cable.
In addition to the foregoing patents, U.S. Pat. No. 3,631,733 discloses an elastic transmission belt of single loop twisted construction, with the looped ends thereof being held together by a metal clip. Also U.S. Pat. No. 4,045,072 discloses an abrasion resistant boot and pendant or sling of wrapped construction.